Creating
the Greek and Trojan Armies
The biggest challenge faced by MPC
during the making of Troy was creating the battle
sequences. At the time of production, MPC did not have Massive
software. They looked into various other solutions
and off-the-shelf software packages, but nothing was suitable
for a project of this scale. Head of Research and Development,
Julian Mann, was tinkering with some ideas for artificial
intelligence (AI), and welcomed the opportunity to explore
this technology.
A team of ten MPC developers worked
solidly from October 2002 to April 2004 to create and support
a bespoke crowd generation system. The system used by MPC
for ‘Troy’ was not a single application, but
a very large suite of tools using Alias Maya as the backbone,
and Pixar’s PRMan for rendering. This meant an enormous
number of plug-ins were needed to handle the interaction
between the technologies used; artificial intelligence,
motion capture data, animation blending, and rendering
among them.
All of our shots began with pre-visualization
defining the way each shot would be filmed. There were
a limited number of extras to stand in as soldiers, and
these were color coded to ultimately highlight the difference
between CG and real soldiers. There were a thousand live
action extras split between two shooting units and we planned
to use around 500 for each scene. In reality, however,
we ended up needing just 200 extras per shot.
The shooting conditions were a challenge – we
were working in Mexico in temperatures of 40-45 degrees
Celsius in the middle of nowhere and without mobile phone
coverage. It was incredibly inhospitable and difficult
at times. It took so long to rig the shots and prep the
extras that it was common to only get one or two shots
filmed per day – the majority with a maximum of just
three takes. Logistically the process was very complicated – everything
required the utmost in pre-planning. It was at this stage
that the pre-visualization really proved its worth because
it had already identified the exact placement of the cameras,
key objects and actors in a scene.
MPC wrote a specific set of tools
for use in pre-visualization to lay out the crowd shots.
The most important one was called PIXIE, and allows
you to perform pseudo crowd simulations very quickly. With PIXIE you
could paint sprites of animated soldiers onto 3D terrain
in Maya. Each sprite would have an animated sequence on
it, such as a walk or run cycle. The key here was to enable
the sprite to be pre-rendered from 30 points of view around
the soldier in a 360 degree circle. Depending on where
the soldier was in relation to the active camera, the sprite
would load the animation from the correct perspective.
The result is a scene is full of soldiers that render extremely
quickly for pre-visualization purposes. This same tool
was also used for creating extras in live action shots.
For example, after the match move team had tracked a plate,
we could paint in soldiers exactly where they were needed.
Once this was approved by the VFX Supervisor, Nick Davis,
we performed the full crowd simulation. |
